The present invention relates to infrared reflecting articles and more particularly to interference coatings which reflect infrared energy.
Infrared reflective coatings are generally known. However, the prior art reflective coatings are either expensive because of the materials used or because many layers are required to obtain the necessary transmission-reflection cut-off. The most common single-layer infrared-reflecting coating is gold. Gold is undesirable as a single layer coating for two reasons. The first reason is the high cost and the second reason is that gold also reflects a large amount of the yellow-red portion of the visible spectrum. Therefore, articles having a gold, single-layer, infrared-reflecting coating transmit little of the visible spectrum. Multi-layer, band-pass filters are efficient and flexible in meeting design requirements of a sharp cut-off point and good transmission in the visible range with low transmission in the infrared range. However, the multi-layer band pass filters of the prior art usually require 20 to 30 layers in the coating and neither the band-width of transmitted light or the band-width of reflected light is very wide. Spurious leaks are also a problem with prior art multi-layer, interference films as well as the difficulty of manufacture and expense associated with producing many superimposed coatings.